The present invention relates to devices for controlling discharge of fuel vapor from vehicle fuel tanks. More particularly, the present invention relates to venting assemblies adapted to use vacuum from an external source to initiate venting of pressurized fuel vapor from a vehicle fuel tank during vehicle operation.
One common problem in the design of vehicle fuel systems is the provision of a sturdy, compact vent assembly adapted to provide generally unrestricted venting of pressurized fuel vapor from the vehicle fuel tank during normal operation of the vehicle. A well-designed venting assembly provides for venting of fuel vapor at relatively high flow rate to a vapor recovery canister or the like to maintain acceptable levels of fuel vapor pressure in the vehicle fuel tank.
In designing assemblies to provide venting at high vapor flow rates, engineers have experimented with a wide variety of valve structures. One convenient alternative is a vent valve which is actuated by vacuum. The vacuum manifold of a typical vehicle engine provides a suitable external vacuum source for such a vent assembly. When the engine is running during normal vehicle operation, a vacuum is established to actuate the vent valve to allow venting of fuel vapor. Vacuum-actuated venting assemblies have been generally located at or near the vacuum manifold of the vehicle engine.
Vapor venting assemblies preferably also perform a variety of additional functions. One function usually provided by a conventional venting assembly is rollover closure. The venting assembly should be designed to quickly close in response to changes in the attitude of the vehicle fuel tank in excess of a predetermined amount, e.g., during rollover of a vehicle in an accident. Rapid closure of the venting assembly is important to prevent leakage of liquid fuel or fuel vapor from the venting assembly. Rollover valve assemblies are generally adapted for mounting directly in fuel tanks.
In addition, venting assemblies are sometimes provided with vacuum-relief valves which open in response to the onset of vacuum conditions in the vehicle fuel tank. When the temperature of the vehicle fuel tank drops the fuel vapor pressure in the vehicle fuel tank can drop to below a predetermined level lower than atmospheric pressure. A vacuum-relief valve is typically configured to allow air to enter the fuel tank, thereby returning the pressure in the vehicle fuel tank to an acceptable level.
Such vacuum-relief valves have been adapted for mounting in the fuel cap installed on a filler neck of a vehicle fuel tank. However, these vacuum-relief valves are typically directly exposed to atmospheric dust during operation. Upon ingestion of the dust, the valves tend to develop leaks and require replacement under warranty protection.
According to the present invention, a vacuum-actuated venting assembly is provided which is adapted to be mounted directly in an aperture in a vehicle fuel tank. The venting assembly includes a hollow housing mounted in the aperture and means for partitioning the hollow housing into a vent chamber exposed to fuel vapor from the vehicle fuel tank and an outlet chamber. The partition means is formed to include a vent opening.
A vent valve is mounted in the housing for movement between a closed position blocking the flow of fuel vapor between the vent chamber and the outlet chamber through the vent opening and an open position allowing flow of fuel vapor from the vent chamber through the vent opening to the outlet chamber. In addition, the apparatus includes means for using vacuum to move the vent valve between the closed position and the open position.
Moreover, the vacuum-actuated venting assembly of the present invention integrates venting with other functions typically performed in conventional tank-mounted venting assemblies. Thus, the venting assembly of the present invention provides a unitary, compact housing adapted to be mounted directly in the fuel tank and designed to include a vacuum-actuated venting feature as well as additional features.
One additional feature of a preferred embodiment of the present invention is a rollover valve assembly which is advantageously adapted to be received in the same housing which contains the vacuum-actuated vent valve. Specifically, the housing is formed to include a valve chamber and a rollover valve assembly is received in the valve chamber for movement therein. The vent assembly further includes second means for providing a partition between the vent chamber and the valve chamber. The second partition means is formed to include a vent opening, and the rollover valve assembly serves as means for blocking flow of fuel vapor and liquid fuel through the second vent opening in response to a change in vehicle attitude in excess of a predetermined amount.
Another feature of preferred embodiments of the present invention is a vacuum-relief assembly. In some embodiments, the vacuum-relief assembly is appended to the vent valve for movement therewith and extends through the vent valve. The vacuum-relief assembly includes a vacuum relief conduit and a relief valve positioned in the vacuum relief conduit. The relief valve is configured to move in response to fuel tank vacuum conditions to an open position allowing air to flow into the fuel tank to relieve the tank vacuum. Under conditions where substantial air flow is required to relieve the tank vacuum condition, the vacuum-relief assembly assists in moving the vent valve to its open position, thereby allowing make-up air flow in reverse flow from the atmosphere past the open vent valve to the fuel tank.
Advantageously, air flowing in reverse flow past the open vent valve must first pass through a vapor recovery canister where dust can be removed from the air. Thus, the potential for dust ingestion by the vacuum-relief valve is substantially reduced.
Moreover, The use of the fuel vapor vent path for reverse air flow allows vacuum relief to occur rapidly--i.e, at high air flow rates. The need for such high air flow is particularly acute when the fuel tank experiences a sudden temperature drop as might occur, e.g., when the vehicle is driven into a car wash where underspray can contact the fuel tank. Advantageously, the present invention provides a high-flow vacuum-relief mechanism specially configured to be integrated into a tank venting assembly.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.